Method of making metaldehyde



Patented Aug. 24, 1943 l a V MA GME -WPE j 1 iliillard Vgel Los ;Angeles ,;dalif, assignor pf i fifty per cent to Paul lifrutantan, Los i lngeles No Drawing. Application octobeeiaisn, ":1 .3:v 1' .J .SerialNo.361,944-z i Y io aims. (omen-2.40)

.The substance described :.under the name metaldehyde. is one of the 'polymerides of acetaldehyde. (CHsCHO), .the latter being commonly known and being referred to herein as aldehyde. Metaldehyde is a:c0l0rless, crystalline solid which is usually assigned the formula.

((321140) 4, on the basis of the characteristics of.

its solutions in phenol, although its solutions in some other solvents have characteristics incon sistent withthisformula. The structural formula for the substance has never been derived.

The material has various technical uses, particularly as a snail poison.-

In the methods of manufacturing metaldehyde heretofore'described it has been necessary to start with substantially pure aldehyde, which is polymerized to metaldehyde by the action of an acid (usually H2804) at very low temperatures.

. unIeSsmaintained at a low temperature.

which may be recovered by filtration or the like, water-'Washed,-*and finally. dried on ma filter through which cold air is passed; The DIECi-Di? tateis likely. to becomegummy and unfilterable The yield .of metaldehyde obtained at point in the process is onlymoderately favorable; however, by further treatment" of the liquid which remains additional quantities of metaldehyde may-.be" obtained. 1- Upon. being allowed to stand for a short period of time, this liquid separates into an aqueous body (consisting of water, alcohol, acid, and a small proportion of unchanged aldehyde) and an oily, supernatant layer consisting substantially of paraldehyde. I separate this supernatant liquid, without any particular care to avoid taking some of the If the acid is applied to the aldehyde at normal temperatures, a difierent polymeride, paraldehyde '(C2H40)3, which is a liquid product having different properties and uses, is formed in a vigorous, strongly exothermicreaction.

I have'discovered that metaldehyde may be produced from cheap or valueless raw materials by so modifying the prior art methods as. to

take advantage of certain peculiarities in. the solubilities of the solid polymer. These raw materials are,for example, thesinglings or first run nings obtained in the distillation of ethanol from fermented molasses and the condensate obtained from the vapor recovery systems now generallyapplied to wine storage tanks. These liquids chilled to about F. or lower.

aqueous material with it, and then'add to it a.

dilute, aqueous solution of a mild alkali, prefer-x ably NaHCOz, in amount sufiicient to neutralize any acid present and to leave the. material somewhat alkaline. During these steps the temperature is permitted to rise to a normal level, per

haps 80 F. The alkaline mixture is agitated strongly for a short period of time and then When the low temperature is reached a second precipitation of metaldehyde occurs, and the precipitate may be be recovered, washed, and dried as above; If

desired, the above-mentioned aqueous body may be distilled to recover ethanol of low aldehyde content.

' The yield of metaldehydemaybe improved by consist mainly of alcohol but contain on the average 7% to 14% of aldehyde whichcan be separated completely only with considerable difiiculty and expense. For this reason they are substantially waste products and sometimes noxious wastes, and are unsuitedfor use as raw Y materials in the prior art methods.

concentrating the aldehyde content of the original raw material, as by adding water to the singlings and rectifying in an efiicient fraction- In utilizing these 'low grade materials I may operate either without or with a preliminary concentration of the aldehyde content.

In operating. without the concentration step, 7

I add to the dilute solution of aldehyde in ethanol a considerable volume of a weakacid,

such as diluted (5%) acetic acidsolutionin water 1 v or highly'diluted sulfuric acid. I then reduce the temperature into a range from 25 top0 F.

and allow the batch to stand for at least an hour,

preferablyabout two hours. No precipitation; occurs underthese conditions, but on theaddition of large volumes of cold water, maintaining,

' the bath at not over 35 R, metaldehydeseparates as a flocculent or granular precipitate ating'colunm. This distillation should be'so controlled as to yield an alcohol-aldehyde mixture containing not less than by weight ot alde-' hyde, and is preferred. There is no object in raising the aldehyde content above 75%. I

To this aldehyde solution in alcohol I add a somewhat diluted sulfuric acid, preferably not over 50% acid-concentration, reducing the tem perature of the bath to about 35 F. Polymerization takes place slowly "but is hastened by the addition of a solid, anhydrous metallic chloride such as calcium chloride or 'zinc chloride. If the temperatureisallowed. to rise above the figure stated, the polymerization is likely to run wild 'and'produce the liquid instead of the solid polymer. f 1 f After sufficient time, which maybe from ten ''minutes .to' two hours, depending on the aldehyde concentration and the quantity of water present,

this

polymerization is complete but, the solid product remains in solution in' the alcohol. But on the addition of about two volumes of ice water, the metaldehyde is thrown out in the solid form and may be purified by washing and drying as above described.' The yield of metaldehydeby this step is muchhigher than the yield of the similar step lpracticed upon unconcentratedsinglingsmnd under ideal conditions it closely approaches the V theoretical. V

aldehyde is converted to paraldehyde, which may I be separated and treated with rallgali-asabove; 1 It appears that there is no practical object in. fractionating the aldehyde-alcohol mixture to a Ordinarily; however, some ,of the higher aldehyde content thanabout '50%,-but I i have so far been unable to obtain from alcoholaldehyde solutions containinglessithan. 45% aldehyde sufficiently improved yields of the "solid polymer to justify the concentration step; I claim as my invention:'

- '1. The gmethod of producing metal'dehyde which comprises: treating an alcoholic solution of :acetaldehyde with:a dilute acid to polymerize the aldehyde content .of said solution; maintaining a temperature :of "to 35 ;F..during'said polymerization to restraintheformation ofparaldiehyde; adding a relatively large volume of cold water to the reacted "solution; separating fromthe aqueous :mixture precipitated metaldehyde and :a supematant .paraldehydic *fraction;

.oracetaldehyde containing not less than 45% by weight-of the aldehyde with-an aqueous-solution.

'*-1ymerization to restrain the formation ofparal v dehyde; andfinally precipitating the solid inetal V dehyde from alcoholic solutionjby addingla r 'fatively large volume of cold Wat?! thereto." Y

agitating said paraldehydic fraction *with .ari; aqueous, mildly alkaline solution at normal tern perature; coolingthe treated paraldehydic frac tion to F.; and separating precipitated meta dehydefrom the cold, alkaline product. a I J p 2. The method of producing metaldehyde which comprises: treating an alcoholic solution r:'j of acetaldehyde witha dilute;aciditoi'polymerize the aldehyde content of said solution; maintain.- ing a temperature of 0? to 35F. during saicl'pjo-V Y 3; The method of producing metald ehy d which comprises: treating an alcoholic solutio of sulfuric acid containing not more than by"? weight of the acid to polymerize the aldehyde- 5 content-of first said solution; maintaining a teinperature not grea'terthan35? during said polye merization; and finally .precipitatingthe solid". metaldehyde from 'alcoholicsolution by adding a relativelydarge volumeof coldwater thereto. 1:1 I

-A 'methodias'and forthe purpose: set forth in claim 3, in zwhichthe polymerization with acid is conducted in'thepresenceof "a" solid an v hydrous metallic salt. 1' v I;

q WILLARD LfVOGEL'. l 

